Concrete is one of the most important building materials employed in modern construction. Concrete's strength, permanency and relatively low cost have made it one of the premier building materials today. Unfortunately, the popularity of concrete as a building material is not without its shortcomings. As many thousands of concrete mixing trucks return to the concrete yard every day, the residual concrete adhered to the walls of the mixing drum must either be retarded to prevent it from setting within the mixing drum, or washed out.
A current method of washing the drum interior involves the addition of approximately 200 liters of an aqueous set retarder solution, rotating and backing-up the rotation of the drum to the point of discharge three times. Next, the truck is parked until the next morning's concrete can be batched on top of the drum. This process resulted in four notorious problems. First, modern concrete drum mixing fins are too tall and will not allow the retarder solution to contact the entire fin surface. Second, 200 liters of solution is often impossible to batch on top of the next morning, especially at plants which used a premier or central mixer. Third, turning the drum back three times is a tedious process which many cement truck operators fail to do properly. Finally, during winter conditions, a 200 liter lump of ice is very hard to deal with.
As a result of these problems, many concrete companies merely rinse the drum with large amounts of water and dump the residual material into a settling pond. This process is riddled with potential environmental hazards to the ground water. Accordingly, a solution to these problems is needed.
U.S. Pat. No. 3,188,238 to Lyon, issued Jun. 8, 1965, discloses a method and apparatus for cleaning chemical tank trucks. The apparatus includes an air pressure driven spray head which is permanently mounted inside the tank, whereby high pressure fluid and air comingle and exit the nozzle openings to form a mist.
U.S. Pat. No. 3,833,011 to McDermott, et al., issued Sep. 3, 1974 discloses a method for cleaning service stations gasoline storage tanks by jet spraying a high viscosity cleaning fluid, such as aqueous cellulose gum solution, by means of a rotating nozzle over the interior surface of the tank with sufficient pressure to break lose rust and hydrocarbon deposits.
U.S. Pat. No. 4,285,808 to Horton, issued Aug. 25, 1981, discloses an elaborate apparatus for the separation of sand, gravel and cement from the washout water resulting from a concrete truck washout.
U.S. Pat. No. 4,341,232 to Maton, issued Jul. 27, 1982, discloses an apparatus for cleaning the interior of milk transporting tankers. The downward motion of a piston rod causes the spray arms of this apparatus to rotate.
U.S. Pat. No. 4,859,249 to Valentini, issued Aug. 22, 1989, discloses a cleaning process for removing material coated on the inner surface of an enclosed vessel, e.g., photographic emulsions, photopolymers, subbing layers, chemicals, etc. The process utilizes a rotating spray head which directs a liquid stream at a pressure of from 4,000 to 8,000 psi in a 360.degree. solid angle using a fixed point as the angle vertex.
U.S. Pat. No. 4,964,917 to Bobrowski et al., issued Oct. 23, 1990 discloses a method of reclaiming leftover ready-mix concrete comprising the steps of (1) retarding the hydration of the unused portion returned from a job site, and (2) after the desired retardation period, adding a hydration acceleration agent to restore the concrete to a settable state.
It is an object of the present invention to provide a method and apparatus for retarding the set of residual concrete with a low amount of solution.
It is also an object of the present invention to provide a simple method for cleaning residual concrete from a concrete-containing vessel.
These and other objects will be described in more detail below.